1. Field of the Invention
The present invention relates generally to explosive compositions, and more particularly to explosives comprising water soluble ammonium salts combined with fuels and sensitizers, commonly referred to as water gel or slurry explosives.
Water gel or slurry explosives are formed by dispersing fuel and sensitizer components in a saturated or unsaturated aqueous solution of an oxidizing salt, typically including ammonium nitrate. Suitable fuels include various hydrocarbons, coal dust, urea, sulfur, and the like, while suitable sensitizers include both explosive compounds, such as trinitrotoluene, and low density components, such as finely divided aluminum, dispersed gas bubbles, microballoons, or finely divided porous solids. In addition to the fuels and sensitizers, water gel explosives require the addition of a gelling agent, such as guar gum, carboxymethyl cellulose, polyacrylamides, and the like. Other components, such as cross-linking agents, may also be added in order to obtain desired characteristics of the explosive.
For use in down hole blasting applications, water gel explosives are typically packaged by pouring the still liquid slurry into small polyethylene bags or "chubs" for loading into the bore holes.
Cross-linking agents added to the slurry act after packaging to thicken the slurry into its final form. A problem has been recognized in water gel explosives having relatively high contents of low density sensitizers, such as flake aluminum. In some cases, the specific gravity of the resulting composition is below 1.0, and the packaged explosive will tend to float in bore holes which are filled with water. While the density may be increased by the addition of high density components, such components have a tendency to settle out of the gel during the mixing and packaging operations.
It would therefore be desirable to provide methods and compositions for suspending high density components in water gel explosives in a manner which limits or prevents their settling out. It would be particularly desirable to provide such methods and compositions which also improve other characteristics of the explosive at the same time.
2. Description of the Background Art
Water gel explosives of the general type of the present invention are generally described in the following U.S. Pat. Nos. 3,819,429 to Schaefer; 4,077,820 to Bolza et al.; and 4,439,254 to Mullay. See in particular U.S. Pat. Nos. 3,819,429 and 4,439,254 which further describe the addition of various densifying agents. U.S. Pat. No. 3,361,603 to Griffith describes the addition of ground paper to explosive compositions of all types in order to reduce the density of the explosive. U.S. Pat. No. 3,507,718 to Mortensen et al., describes the addition of fibrous fuels, such as wood pulp and ground alfalfa, which may be treated with water repellents so that they can establish tiny gas or air pockets and serve as sensitizers. U.S. Pat. No. 4,140,561 to Keith et al. describes the addition of fibrous materials, and in particular synthetic fibers such as rayon, and polyethylene, in order to improve the stability and increase the viscosity of the resulting explosive composition. U.S. Pat. No. 4,435,232, to Ciaramitaro et al., describes the addition of processed cellulose, such as comminuted paper, to liquid-based explosives, such as nitroglycerine dynamite, to form a water-resistant composition.